Cured elastomeric materials have a desirable set of physical properties typical of the elastomeric state. They show a high tendency to return to their original sized and shape following removal of a deforming force, and they retain physical properties after repeated cycles of stretching, including strain levels up to 1000%. Based on these properties, the materials are generally useful for making shaped articles such as seals and gaskets.
Because they are thermoset materials, cured elastomeric materials can not generally be processed by conventional thermoplastic techniques such as injection molding, extrusion, or blow molding. Rather, articles must be fashioned from elastomeric materials by high temperature curing and compression molding. Although these and other rubber compounding operations are conventional and known, they nevertheless tend to be more expensive and require higher capital investment than the relatively simpler thermoplastic processing techniques. Another drawback is that scrap generated in the manufacturing process is difficult to recycle and reuse, which further adds to the cost of manufacturing such articles.
Articles made from elastomeric materials, such as seals and gaskets, may be subject to a wide variety of challenging environmental conditions, including exposure to high temperature, contact with corrosive chemicals, and high wear conditions during normal use. For example, bearing seals for automotive applications see high temperature in normal use and are exposed to lubricating fluids containing basic compounds and other corrosive materials. They are also subject to wear and abrasion from the moving parts they act to seal. Accordingly, it is desirable to make such articles from materials that combine elastomeric properties and stability or resistance to the environmental conditions.
Crosslinked polyurethane materials have excellent physical properties, such as high tensile strength and wear resistance, compared with other cross linked elastomeric materials. However, they are usually limited to a continuous service temperature of only up to about 100° C. In some applications, the relatively low heat resistance of the polyurethane materials is a drawback that narrows the potential use of the materials. For example, they are generally unsuitable for use in some automotive applications, where the in service use can be 150° C. or higher.
It would therefore be desirable to provide materials having excellent physical properties in combination a high level of heat resistance. In addition, it would be desirable to provide such materials that are readily recyclable and that can be processed by conventional thermoplastic processing techniques.